The art is replete with descriptions of the use of myriad phenothiazine derivatives as lubricant antioxidants. Some of the many phenothiazine derivatives have alkyl substituents on the aromatic moiety of the phenothiazine; others on the nitrogen; and still others on both. Suggestions also have been made to use mixtures of diphenylamines and phenothiazines as lubricant antioxidants in the search for improved lubricant compositions.
Notwithstanding the satisfactory performance achieved by some lubricant compositions containing phenothiazine antioxidants, there remains a need for lubricant compositions that will meet ever more stringent requirements of lubricant users.
Indeed, one objective of the present invention is to enhance the rust inhibition and antiwear properties of lubricant compositions.
Another objective of the present invention is to provide a lubricant with enhanced antioxidation properties.